This invention relates to an engine starter and, more particularly, to a coaxial engine starter in which an output rotary shaft driven by an electric motor is axially slidable so that a pinion gear disposed on a front end of the output rotary shaft can be brought into engagement with an engine ring gear.
One example of a conventional coaxial engine starter for starting an internal combustion engine is disclosed in Japanese Kokai No. 63-90665. According to the conventional coaxial engine starter 1 shown in FIG. 1, a d.c. electric motor 2 has a hollow armature rotary shaft 3 and a solenoid switch 4 positioned at the rear end of the d.c. motor 2 and an output rotary shaft 5 coaxially disposed at the front end of the armature rotary shaft 3. The output rotary shaft 5 is axially slidably and rotatably supported by a bearing 6 disposed within the armature rotary shaft 3, whereby the output rotary shaft 5 can be pushed forward when the unillustrated push rod of the solenoid switch is actuated.
It is seen that a sun gear 7a is formed on the outer circumference of the front end of the armature rotary shaft 3 and a plurality of planetary gears 7b are in mesh with the sun gear 7a. These planetary gears 7b also mesh with an inner gear 7c formed in the inner circumferential surface of the front bracket 8 and are rotatably supported by shafts 7d secured on a carrier 7e which is an integral part of a clutch outer member 9b of an over-running clutch 9. The sun gear 7a, the planetary gears 7b, the inner gear 7c, the shafts 7d and the carrier 7e together constitute a planetary speed reduction gear 7 which reduces the rotational speed of the armature rotary shaft 3.
On the output rotary shaft 5, an over-running clutch 9 is mounted, of which clutch inner member 9a is engaged at its splines 9d with the output rotary shaft 5 by helical splines 5a, so that the output rotary shaft 5 is allowed to axially slide while being rotated by the clutch inner member 9a. A bearing 15 is disposed between the inner ends of the clutch inner and outer members. A compression spring 9e is disposed between the clutch inner member 9a and the splined portion 5a of the output rotary shaft 5. On the front end of the output rotary shaft 5, a pinion 10 which engages and disengages relative to an engine ring gear (not shown) is mounted by straight splines 10a formed in the inner circumference of the pinion 10 and splines 5b formed on the outer circumference of the output rotary shaft 5. A stopper 12 is mounted on the output rotary shaft 5 by a stop ring 13. A compression spring 14 is disposed between a step of the pinion 10 and a step portion of the output rotary shaft 5. When the output rotary shaft 5 is moved forward, the pinion 10 meshes with the engine ring gear (not shown) to rotate and start the engine.
In the coaxial engine starter 1 of the above construction, the over-running clutch 9 and the planetary speed reduction gear 7 are assembled into one unit through which the output rotary shaft 5 extends in an axially aligned relationship. This assembly of the over running clutch 9 and the planetary speed reduction gear 7 is supported only at the front end of the clutch inner member 9a which is simply inserted into the bearing 11 supported by the front bracket 8. Thus, since this assembly is supported in a cantilevered fashion, the rotary axes of the planetary gears 7b supported by the pins 7d secured to the carrier 7e integral with the clutch outer member 9b wobble or become eccentric, resulting in the generation of noise in the meshing gears, the generation of wear in the tooth meshing surfaces, and damage to the gears.